Anyone know.. if Sunrace 8 speed cassette cogs are interchangeable with Shimano hyperdrive cogs? IE: could they be used in the 'stack'.. so to speak? I'm aware of rear derailleur specs etc.. possible shifting indexing issues. Or the reverse... Shimano into a Sunrace unit... ?

Well, given that Sheldon has been dead a good number of years and the bike industry continues to make changes to their designs, it doesn't seem odd that you're going to come across statements that may have been true at the time but don't apply to all applications, everywhere, for all time.

The answer to your original question seems to be...no one here is sure. Why don't you figure it out and tell us your know-ledge.